The present invention relates to a method and apparatus for automatically detecting the format of a television signal at a video encoder to allow proper encoding of the signal. The invention is particularly suited for detecting high-definition television (HDTV) formats.
The communication of digital video, audio, and other data has become increasingly common due to the improved fidelity, bandwidth efficiency, and versatility of digital signals relative to analog signals. For example, many digital television broadcast systems deliver digital television signals to users' homes via direct satellite broadcasts. Moreover, terrestrial broadcast of digital television signals is also expected to gain widespread acceptance.
The television or other digital data may be obtained via various methods. For example, a broadcaster may have a local library of digital television programs or other data which is stored on magnetic storage media such as magnetic tape, or optical storage media, such as compact disc, digital video disc, or laser disc. The broadcaster may also receive digital television or other data from another transmission source, including, for example, a satellite distribution network, a terrestrial broadcast network, or a microwave distribution network.
The video data may be digitized, compressed and encoded when it is obtained, e.g., at a television studio, or may be compressed subsequently, e.g., at a satellite uplink station. Moreover, the video data may be stored in a compressed or uncompressed state. Generally, compression involves transforming data samples in the pixel domain to a spatial frequency domain, quantizing, and coding using differential coding and Huffman encoding. The encoded data is then multiplexed with other video signals in a digital transport data stream. Motion compensation and estimation may also be used in the pixel domain to provide further compression.
However, for proper compression and encoding, the format of the video data must be known. Currently, various formats of HDTV are specified in the Advanced Television Systems Committee's (ATSC) digital television standard which is adopted by the Federal Communications Commission (FCC) as the digital television broadcasting standard in the United States. The HDTV formats include:
(1) 1920.times.1080.times.60 frames per second progressive scan, with a pixel sampling frequency of 148.5 MHz; PA1 (2) 1920.times.1080.times.59.94 frames per second progressive scan, with a pixel sampling frequency of 148.5/1.001=148.35 MHz; PA1 (3) 1920 horizontal pixels.times.1080 lines.times.30 fields per second interlaced scan (e.g., 540 lines per field), with a pixel sampling frequency of 74.25 MHz; PA1 (4) 1920 horizontal pixels.times.1080 lines.times.29.97 fields per second interlaced scan (e.g., 540 lines per field), with a pixel sampling frequency of 74.25/1.001=74.175 MHz; PA1 (5) 1920 horizontal pixels.times.1080 lines.times.24 frames per second progressive scan, with a pixel sampling frequency of 74.25 MHz; PA1 (6) 1920 horizontal pixels.times.1080 lines.times.23.98 frames per second progressive scan, with a pixel sampling frequency of 74.25/1.001=74.175 MHz; PA1 (7) 1920.times.1080.times.30 frames per second progressive scan, with a pixel sampling frequency of 74.25 MHz; PA1 (8) 1920 horizontal pixels.times.1080 lines.times.29.97 frames per second progressive scan, with a pixel sampling frequency of 74.25/1.001=74.175 MHz; PA1 (9) 1920.times.1080.times.25 frames per second progressive scan, with a pixel sampling frequency of 74.25 MHz; PA1 (10) 1280 horizontal pixels.times.720 lines.times.60 frames per second progressive scan, with a pixel sampling frequency of 74.25 MHz; and PA1 (11) 1280 horizontal pixels.times.720 lines.times.59.94 frames per second progressive scan, with a pixel sampling frequency of 74.25/1.001=74.175 MHz.
Note that pixel numbers refer to active pixels, and lines per frame or field refer to active lines. The 1920.times.1080 formats are discussed in the document SMPTE 274M, entitled "Proposed SMPTE Standard for Television--1920.times.1080 Scanning and Analog and Parallel Digital Interfaces for Multiple-Picture Rates." The 1280.times.720 formats are discussed in the document SMPTE 296M, entitled "SMPTE Standard for Television--1280.times.720 Scanning, Analog and Digital Representation and Analog Interface."
Compressed HDTV data formats may be governed by the MPEG-2 standard, described in document ISO/IEC 13818-2, entitled "Information Technology--Generic Coding of Moving Pictures and Associated Audio, Recommendation H.262."
HDTV formats at 30/29.97 frames per second have gained acceptance in the United States, while European HDTV formats may employ 25 frames per second.
Additionally, digital standard definition television (SDTV) formats include NTSC at 30 frames per second, and 525 lines per frame, and PAL at 25 frames per second, and 625 lines per frame.
Previously, when video data having different formats was compressed and encoded, a user command was necessary to inform the encoder of the current video format as well as subsequent changes in the video format. For example, the video format might change when a live television broadcast is followed by a recorded movie on a television channel. This procedure is inefficient, unreliable, and inconvenient.
Accordingly, it would be desirable to provide a system which automatically detects the format of a video source, including HDTV video as well as SDTV, and progressive as well as interlaced scan. The system should be compatible with video standards such as SMPTE and video compression standards such as MPEG-2.
The present invention provides a system having the above and other advantages.